In radio frequency (RF) signal transmission lines, typically transmitting electromagnetic signals with the frequencies over 1 MHz, undesirable effects can occur if a strong surge (e.g., caused by lightning) is transmitted to sensitive electronic devices coupled to the transmission line. Lightning can produce strong surge signals ranging in frequency from 0 (direct current) to 1 MHz. Therefore, a surge suppressor should prevent surges of low frequency signals from passing through the transmission line, while allowing the desired RF signals to pass freely.
Surge suppressors insertable into a transmission line in series with the equipment being protected can employ quarter wave stubs (QWS) which are seen as a short circuit to the ground by low frequency signals, while RF signals encounter input impedance corresponding to an open circuit.
Traditional QWS surge suppressors usually have very narrow bandwidth of the RF signals allowed to pass. Besides, the surge signals that can be allowed to pass by the traditional QWS surge suppressors can have energy levels which are dangerous for sensitive electronic equipment connected to the transmission line. Known enhancements intended to improve the bandwidth and the let-through energy usually introduce an element insertable into the communication line in series with the QWS, thus rendering the surge suppressor asymmetrical, i.e., requiring a unidirectional insertion of the modified QWS surge suppressor into the communication line. The asymmetrical insertion requirement can significantly increase the rate of installation errors.
Thus, a need exists for a surge suppressor which has a relatively wide pass through signal bandwidth with a return loss value more than 20 dB, low let-through energy and very high surge attenuation levels for low frequency signals. The need also exists for a surge suppressor which is symmetrically insertable into a communication line.